Falling film heat exchangers usually include an array of vertical tubes. The tubes can be exposed or surrounded by a shell. The process liquid can be either inside or outside the tube with the heat exchange liquid on the other side.
Although falling film heat exchangers are often used to heat a liquid feed stream, they can be used for cooling such a stream. Falling film heat exchangers of the described types can be used as freeze exchangers for producing fresh water from brackish water and seawater, for concentrating fruit and vegetable juices, and in industrial crystallization processes. See U.S. Pat. No. 4,286,436. As the liquid flows through each tube, it can be cooled enough to crystallize a solid from the liquid. Thus, by cooling seawater, ice is obtained which when separated, washed and melted provides potable water. When a fruit or vegetable juice is similarly chilled, ice forms and is removed to provide a concentrated juice.
Freeze exchangers of the described type can use any cooling liquid to cool a process or feed liquid flowing downwardly in or outside the tubes. Some suitable cooling fluids are refrigerants such as ammonia and Freon brand refrigerants.
Whether the heat exchanger is used to heat or cool a process or feed liquid, it is desirable to be able to control the thickness and uniformity of the falling film on each tube external surface, whether the falling film is a feed liquid or a heat exchange liquid. Existing apparatus, however, does not adequately control or regulate the falling film thickness in an economic manner. There is a need, accordingly, for apparatus which will facilitate supplying the process or feed liquid, or the heat exchange liquid, to the exterior surface of the tubes to produce falling films of uniform thickness and evenly distributed on the exterior surface of each tube in a relatively inexpensive and simple manner.